1. Field of the Invention
This invention relates to the treatment of polyester cord to improve the bonding properties thereof when utilized as the reinforcing element in the fabrication of vulcanized rubber structures.
2. Description of the Prior Art
In the manufacture of vulcanized rubber goods reinforced with filamentary elements, particularly exemplary of which are pneumatic tires and power transmission belts, the serviceability of the resultant structures largely depends upon the strength of the adhesive bond formed between the reinforcing elements and the rubber in the course of the vulcanization step. The problem of adhesion is especially in the forefront in the manufacture of motor vehicle tires since the severe service conditions to which the structures are subjected can result in the development of extremely high temperatures and enormous dynamic stresses therein which in turn are prone to cause separation or delamination of the reinforcing element from the rubber.
The present state of the art with respect to tire cord adhesives irrespective of whether such reinforcer is polyester, nylon or steel is represented by the so-called two-dip system wherein the reinforcing element is provided with a first coating in the form of a polyoxazolidone resin and then a subsequent coating of a RFL adhesive. In accordance with this prior art, the first adhesive layer is obtained by coating the reinforcing element with an aqueous dispersion of a blocked aromatic diisocyanate and a polyepoxide and thereupon effecting the cure of these reactants in order to secure the indicated resinous structure. The aforementioned system is difficult to fault from the standpoint of the degree of adhesion it promotes. A significant disadvantage of the system, however, resides in the fact that processing problems are encountered in obtaining a uniform coating of the first applied reactive components since it is difficult to maintain a uniform dispersion of the polyisocyanate. Accordingly, there is a need for a like adhesion promoting system but wherein a preformed polymer serving as a polyisocyanate precursor is utilized in the first dip operation instead of the conventional aromatic disisocyanate.